Method for transmitting uplink and wireless device using same

ABSTRACT

A method for uplink transmission in a wireless communication system. A user equipment (UE) determines whether to transmit or drop a sounding reference signal (SRS) on a last symbol in a i th  subframe. The SRS is dropped if multiple timing advance groups (TAGs) are configured, if a portion of the last symbol of the i th  subframe for transmitting the SRS toward a first serving cell in a first TAG is overlapped with an (i+1) th  subframe for transmitting an uplink channel toward a second serving cell in a second TAG and if a total power of the SRS and the uplink channel exceeds a maximum value on the overlapped portion of the last symbol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/257,218 filed on Sep. 6, 2016, which is a Continuation of U.S. patentapplication Ser. No. 14/835,036 filed on Aug. 25, 2015 (now U.S. Pat.No. 9,461,797 issued on Oct. 4, 2016), which is a Continuation of U.S.patent application Ser. No. 14/112,213 filed on Oct. 16, 2013 (now U.S.Pat. No. 9,137,762 issued on Sep. 15, 2015), which is filed as theNational Phase of PCT/KR2012/007890 filed on Sep. 28, 2012, which claimsthe benefit under 35 U.S.C. § 119(e) to U.S. Provisional ApplicationNos. 61/681,636 filed on Aug. 10, 2012, 61/678,120 filed on Aug. 1,2012, 61/667,935 filed on Jul. 3, 2012, 61/645,566 filed on May 10,2012, 61/644,439 filed on May 9, 2012, 61/613,467 filed on Mar. 20,2012, 61/611,590 filed on Mar. 16, 2012, 61/591,279 filed on Jan. 27,2012, 61/554,493 filed on Nov. 1, 2011, and 61/541,044 filed on Sep. 29,2011, and under 35 U.S.C. § 119(a) to Korean Patent Application No.10-2012-0108365 filed on Sep. 27, 2012, all of which are herebyexpressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION

The present invention disclosed herein relates to wirelesscommunication, and more particularly, to a method and device fortransmitting an uplink in a wireless communication system.

The 3rd Generation Partnership Project (3GPP) long term evolution (LTE),which is an advanced version of Universal Mobile TelecommunicationsSystem (UMTS), is specified in the 3GPP release 8. The 3GPP LTE usesorthogonal frequency division multiple access (OFDMA) in a downlink anduses Single Carrier-frequency division multiple access (SC-FFDMA) in anuplink. The 3GPP LTE adopts MIMO with up to four antennas. Recently,3GPP LTE-Advanced (LTE-A), which is an evolution of the 3GPP LTE, isunder discussion.

As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, a physical channel in the 3GPP LTE/LTE-A is divided into adownlink channel (i.e. Physical Downlink Shared Channel (PDSCH) andPhysical Downlink Control Channel (PDCCH), and an uplink channel (i.e.Physical Uplink Shared Channel (PUSCH) and Physical Uplink ControlChannel (PUCCH).

In order to reduce the interference caused by uplink transmissionbetween terminals, it is important for a base station to maintain uplinktime alignment for a terminal. A terminal may be located in an arbitraryarea within a cell, and a reaching time (the time that an uplink signaltransmitted by a terminal takes to reach a base station) may varydepending on the position of each terminal. The reaching time of aterminal located at a cell edge is longer than that of a terminallocated at the middle of a cell. On the contrary, the reaching time of aterminal located at the middle of a cell is shorter than that of aterminal located at a cell edge.

In order to reduce the interference between terminals, it is necessaryfor a base station to arrange a schedule to allow uplink signalstransmitted by terminals in a cell to be received within each timeboundary. A base station is required to appropriately adjust thetransmission timing of each terminal depending on the situation thereof,and this adjustment is called uplink time alignment. A random accessprocess is a process for maintaining the uplink time alignment. Aterminal obtains a time alignment value (or timing advance (TA)) throughthe random access process, and then, applies the time alignment value soas to maintain the uplink time alignment.

Recently, in order to provide a higher data transfer rate, a pluralityof serving cells has been introduced. However, under the assumption thatfrequencies between serving cells are adjacent or propagationcharacteristics between serving cells are similar, the same timealignment value has been applied to all serving cells.

In existing wireless communication systems, uplink transmission isdesigned in consideration of only the same time alignment value.However, since serving cells having different propagationcharacteristics are allocated in some cases, uplink transmission needsto be designed in consideration of having different time alignmentvalues between cells.

SUMMARY OF THE INVENTION

The present invention provides a method of transmitting an uplinkbetween a plurality of timing advance (TA) groups, and a wireless deviceusing the same.

In an aspect, a method of transmitting an uplink is provided. The methodmay comprise determining a first radio resource on which a soundingreference signal (SRS) is to be transmitted to a first serving cell anddetermining a second radio resource on which an uplink channel is to betransmitted to a second serving cell. The first radio resource and thesecond radio resource may overlap entirely or partially. The method maycomprise dropping the transmission of the SRS and transmitting theuplink channel on the second radio resource to the second serving cell,if in an overlapped radio resource a total transmit power with respectto the SRS and the uplink channel exceeds a maximum transmit power. Thefirst serving cell may belong to a first Timing Advance (TA) group andthe second serving cell may belong to a second TA group different fromthe first serving cell.

The uplink channel may include at least one of a Physical Uplink SharedChannel (PUSCH), a Physical Uplink Control Channel (PUCCH), and asounding reference signal (SRS).

The first and second radio resources may include at least one oforthogonal frequency division multiplexing (OFDM) symbol, and theoverlapped portion may include at least one OFDM symbol.

Each of the first TA group and the second TA group may include at leastone serving cell to which the same TA is applied.

In another aspect, a wireless device for transmitting an uplink isprovided. The wireless device includes: a radio frequency (RF) unit fortransmitting and receiving a radio signal; and a processor connected tothe RF unit, and configured to determine a first radio resource on whicha sounding reference signal (SRS) is to be transmitted to a firstserving cell and determine a second radio resource on which an uplinkchannel is to be transmitted to a second serving cell. The first radioresource and the second radio resource overlap entirely or partially.The processor is configured to instruct the RF unit to drop thetransmission of the SRS and transmit the uplink channel on the secondradio resource to the second serving cell, if in an overlapped radioresource a total transmit power with respect to the SRS and the uplinkchannel exceeds a maximum transmit power. The first serving cell maybelong to a first Timing Advance (TA) group and the second serving cellmay belong to a second TA group different from the first serving cell.

When a plurality of timing advance (TA) groups are configured, theambiguity of the uplink transmission between each TA group can bereduced, and the maximum transmit power of a terminal can be preventedfrom being exceeded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a downlink radio frame in the 3GPPLTE.

FIG. 2 is a flowchart illustrating a random access process in 3GPP LTE.

FIG. 3 illustrates a random access response.

FIG. 4 illustrates an example of a multiple carrier.

FIG. 5 illustrates a UL propagation difference between a plurality ofcells.

FIG. 6 illustrates an example of when a TA between a plurality of cellsis changed.

FIG. 7 illustrates UL transmission according to an embodiment of thepresent invention.

FIG. 8 illustrates UL transmission according to an embodiment of thepresent invention.

FIG. 9 illustrates UL transmission according to another embodiment ofthe present invention.

FIG. 10, including view (a) and view (b), illustrates PUSCH and SRStransmission according to a typical technique.

FIG. 11 illustrates PUSCH and SRS transmission when a plurality of TAgroups are configured.

FIG. 12 illustrates UL transmission according to another embodiment ofthe present invention.

FIG. 13 is a block diagram of a wireless communication system accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A wireless device may be fixed or may have mobility, and may be referredto as another term such as a User Equipment (UE), a mobile station (MS),a user terminal (UT), a subscriber station (SS), or a mobile terminal(MT). In general, the base station may refer to a fixed stationcommunicating with a wireless device, and also may be referred to asanother term such as an evolved-NodeB (eNB), a Base Transceiver System(BTS), or an Access Point.

Hereinafter, it will be described that the present invention is appliedbased on 3rd Generation Partnership Project (3GPP) long term evolution(LTE) or 3GPP LTE-Advanced (LTE-A). This is for exemplary purposes, andthe present invention may be applicable to various wirelesscommunication systems. Hereinafter, LTE includes the LTE and/or theLTE-A.

FIG. 1 illustrates a structure of a downlink radio frame in the 3GPPLTE. This may refer to paragraph 6 of 3GPP TS 36.211 V8.7.0 (2009-05)“Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channelsand Modulation (Release 8)”.

A radio frame includes 10 subframes numbered with indices 0 to 9. Onesubframe includes two consecutive slots. The time required to transmitone subframe is called a transmission time interval (TTI). For example,the length of one subframe may be 1 ms and the length of slot may be 0.5ms.

One slot may include a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time zone. Since the 3GPP LTE usesorthogonal frequency division multiple access (OFDMA) in a downlink(DL), the OFDM symbol is only to express one symbol period in a timezone and thus does not limit a multiple access scheme or name. Forexample, the OFDM symbol may be called different names such as a singlecarrier-frequency division multiple access (SC-FDMA) symbol and a symbolperiod.

Although it is exemplarily described that one slot includes 7 OFDMsymbols, the number of OFDM symbols in one slot may vary depending onthe length of a Cyclic Prefix (CP). According to 3GPP TS 36.211 V8.7.0,one slot in a regular CP includes seven OFDM symbols and one slot in anextended CP includes six OFDM symbols.

A resource block (RB) is a resource allocation unit and includes aplurality of subcarriers in one slot. For example, if one slot includesseven OFDM symbols in a time zone and a RB includes twelve subcarriersin a frequency domain, one RB may include 7×12 resource elements (REs).

A DL subframe is divided into a control region and a data region in atime zone. The control region includes up to three OFDM symbols in thefront of a first slot in a subframe, but the number of OFDM symbols inthe control region may vary. A Physical Downlink Control Channel (PDCCH)and another control channel are allocated to the control region and aPDSCH is allocated to the data region.

As disclosed in 3GPP TS 36.211 V8.7.0, a physical channel in the 3GPPLTE may be divided into a data channel (i.e. a Physical Downlink SharedChannel (PDSCH) and a Physical Uplink Shared Channel (PUSCH)) and acontrol channel (i.e. a Physical Downlink Control Channel (PDCCH), aPhysical Control Format Indicator Channel (PCFICH), a PhysicalHybrid-ARQ Indicator Channel (PHICH), and a Physical Uplink ControlChannel (PUCCH)).

The PCFICH transmitted from the first OFDM symbol of a subframe carriesa control format indicator (CFI) for the number of OFDM symbols (i.e.the size of a control region) used for the transmission of controlchannels in the subframe. A terminal receives the CFI first on thePCFICH and then monitors the PDCCH.

Unlike the PDCCH, the PCFICH does not use blind decoding and istransmitted through the fixed PCFICH resource of a subframe.

The PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for a hybrid automaticrepeat request (HARQ). The ACK/NACK signal for uplink (UL) data on thePUSCH, which is transmitted by a terminal, is transmitted on the PHICH.

A Physical Broadcast Channel (PBCH) is transmitted from the front fourOFDM symbols of the second slot in the first subframe of a radio frame.The PBCH carries system information essential when a terminalcommunicates with a base station, and the system information transmittedthrough the PBCH is called a master information block (MIB). Compared tothis, the system information, which is transmitted on the PDSCHindicated by the PDCCH, is called a system information block (SIB).

The control information transmitted through the PDCCH is called asdownlink control information (DCI). The DCI may include the resourceallocation of a PDSCH (also, referred to as DL grant), the resourceallocation of a PUSCH (also, referred to as UL grant), a set of transmitpower control commands on each UE in an arbitrary UE group, and/or theactivation of a Voice over Internet Protocol (VoIP).

The 3GPP LTE uses blind decoding to detect a PDCCH. The blind decodingdemasks a desired identifier on CRC of a received PDCCH (also, referredto as a candidate PDCCH), and checks CRC errors in order to confirmwhether a corresponding PDCCH is its control channel.

A base station determines a PDCCH format according to DCI to betransmitted to a terminal, attaches Cyclic Redundancy Check (CRC) to theDCI, and then, masks a unique identifier (also, referred to as a RadioNetwork Temporary Identifier (RNTI)) on the CRC according to the owneror purpose of a PDCCH.

The control region in a subframe includes a plurality of control channelelement (CCEs). The CCE is a logical allocation unit used to provide anencoding rate according to a state of a radio channel to a PDCCH andcorresponds to a plurality of resource element groups (REGs). The REGincludes a plurality of resource elements. According to a linkagebetween the number of CCEs and an encoding rate provided by the CCEs,the format of a PDCCH and the number of available bits in the PDCCH aredetermined.

One REG includes four REs and one CCE includes nine REGs. In order toconfigure one PDCCH, {1, 2, 4, and 8} CCEs may be used and an element ofeach of {1, 2, 4, and 8} CCEs is referred to as a CCE aggregation level.

A base station determines the number of CCEs used for the transmissionof a PDDCH according to a channel state. For example, one CCE may beused for PDCCH transmission to a terminal having a good DL channelstate. Eight CCEs may be used for PDCCH transmission to a terminalhaving a poor DL channel state.

A control channel configured with one or more CCE performs interleavingby a REG unit, and after a cell identifier (ID) based cyclic shift isperformed, is mapped into a physical resource.

According to 3GPP TS 36.211 V8.7.0, a DL channel includes a PUSCH, aPUCCH, a Sounding Reference Signal (SRS), and a Physical Random AccessChannel (PRACH).

The PUCCH supports a multi-format. According to a modulation schemedepending on the PUCCH format, a PUCCH having the different number ofbits per subframe may be used. A PUCCH format 1 is used for thetransmission of a Scheduling Request (SR), a PUCCH format 1a/ab is usedfor the transmission of an ACK/NACK signal for a HARQ, a PUCCH format 2is used for the transmission of a CQI, and a PUCCH format 2a/2b is usedfor the simultaneous transmission of CQI and an ACK/NACK signal. Whenonly the ACK/NACK signal is transmitted in a subframe, the PUCCH format1a/1b is used, and when the SR is transmitted alone, the PUCCH format 1is used. When the SR and ACK/NACK are simultaneously transmitted, thePUCCH format 1 is used, and an ACK/NACK signal is modulated andtransmitted in a resource allocated to the SR.

Hereinafter, Sounding Reference Signal (SRS) transmission will bedescribed.

The SRS transmission is divided into periodic SRS transmission andaperiodic SRS transmission. The periodically transmitted SRS istransmitted in a subframe triggered by a periodic SRS configuration. Theperiodic SRS configuration includes an SRS periodicity and an SRSsubframe offset. Once a periodic SRS configuration is given, a terminalmay transmit an SRS periodically in a subframe that satisfies theperiodic SRS configuration.

The aperiodically transmitted SRS means an SRS is transmitted when anSRS request of a base station is detected. In order for the aperiodicSRS transmission, an SRS configuration is given in advance. The SRSconfiguration also includes an SRS periodicity TSRS and an SRS subframeoffset TOffset.

An SRS request for triggering the aperiodic SRS transmission may beincluded in a DL grant or a UL grant on a PDCCH. For example, if an SRSrequest is one bit, ‘0’ represents a negative SRS request and ‘1’represents a positive SRS request. If an SRS request is two bits, ‘00’represents a negative SRS request and the remaining represents apositive SRS request. However, one of a plurality of SRS configurationsfor SRS transmission may be selected.

If a DL grant or a UL grant does not include a CI, a SRS may betransmitted to a serving cell of a PDCCH, where an SRS request isdetected. If a DL grant or a UL grant includes a CI, an SRS may betransmitted to a serving cell indicated by the CI.

It is assumed that a positive SRS request is detected in a subframe n ofa serving cell c. When a positive SRS request is detected, an SRS istransmitted in the first subframe that satisfies n+k, k>4 and T_(SRS)>2in Time Division Duplex (TDD) and (10*n_(f)+k_(SRS)−T_(offset)) modT_(SRS)=0 in Frequency Division Duplex (FDD). In the FDD, a subframeindex k_(SRS) is {0, 1, . . . , 9} in a frame n_(f). In the TDD, asubframe index k_(SRS) is defined in a predetermined table. In the TDDwhere T_(SRS)=2, an SRS is transmitted from the first subframe thatsatisfies (k_(SRS)−T_(offset))mod 5=0.

Hereinafter, a subframe in which an SRS is transmitted is referred to asan SRS subframe or a triggered subframe. In the periodic SRStransmission and the aperiodic SRS transmission, an SRS may betransmitted in a UE-specific SRS subframe.

The position of an OFDM symbol in which an SRS is transmitted may befixed in an SRS subframe. For example, an SRS may be transmitted in thelast OFDM symbol of an SRS subframe. The OFDM symbol in which an SRS istransmitted is called a sounding reference symbol.

Hereinafter, maintaining UL time alignment in the 3GPP LTE will bedescribed.

In order to reduce the interference caused by UL transmission betweenterminals, it is important for a base station to maintain UL timealignment of a terminal. A terminal may be located in an arbitrary areawithin a cell, and the reaching time that an uplink signal that aterminal transmits takes time to reach a base station may vary dependingon the position of each terminal. The reaching time of a terminallocated at a cell edge is longer than that of a terminal located at themiddle of a cell. On the contrary, the reaching time of a terminallocated at the middle of a cell is shorter than that located at a celledge.

In order to reduce the interference between terminals, it is necessaryfor a base station to arrange a schedule to allow UL signals thatterminals in a cell transmit to be received within each time boundary. Abase station is required to appropriately adjust the transmission timingof each terminal depending on the situation thereof, and this adjustmentis called time alignment maintenance.

One method of managing time alignment includes a random access process.A terminal transmits a random access preamble to a base station. Thebase station calculates a time alignment value for fast or slowtransmission timing of the terminal on the basis of the received randomaccess preamble. Then, the base station transmits a random accessresponse including the calculated alignment value to the terminal. Theterminal updates the transmission timing by using the time alignmentvalue.

As another method, a base station receives an SRS periodically orarbitrarily from a terminal, calculates a time alignment value of theterminal through the SRS, and then, notifies it to the terminal througha MAC control element (CE).

The time alignment value is information transmitted from a base stationto a terminal in order to maintain UL time alignment, and a TimingAlignment Command indicates the information.

In general, since a terminal has mobility, the transmission timing ofthe terminal may vary according to the moving speed and position of theterminal. Accordingly, the time alignment value that the terminalreceives may be effective for a specific time. For this, a TimeAlignment Timer is used.

After receiving a time alignment value from a base station and thenupdating time alignment, a terminal starts or restarts a time alignmenttimer. Only when the time alignment timer operates, UL transmission isavailable in the terminal. A value of the time alignment timer may benotified from a base station to a terminal through system information oran RRC message such as a Radio Bearer Reconfiguration message.

When the time alignment timer expires or does not operate, under theassumption that a base station is out of time alignment, a terminal doesnot transmit any UL signal except for a random access preamble.

FIG. 2 is a flowchart illustrating a random access process in 3GPP LTE.The random access process is used for a terminal to obtain UL alignmentwith a base station or to receive a UL radios resource allocated.

A terminal receives a root index and a physical random access channel(PRACH) configuration index from a base station. Each includes 64candidate random access preambles defined by a Zadoff-Chu (ZC) sequence,and the root index is a logical index for a terminal to generate the 64candidate random access preambles.

The transmission of a random access preamble is limited to a specifictime and a frequency resource in each cell. The PRACH configurationindex indicates a specific subframe and a preamble format available forthe transmission of a random access preamble.

Table 1 below is one example of a random access configuration disclosedin paragraph 5.7 of 3GPP TS 36.211 V8.7.0 (2009-05).

TABLE 1 PRACH Preamble System configuration index format frame numberSubframe number 0 0 Even 1 1 0 Even 4 2 0 Even 7 3 0 Any 1 4 0 Any 4 5 0Any 7 6 0 Any 1, 6

A terminal transmits an arbitrarily-selected random access preamble to abase station in operation S110. The terminal selects one of 64 candidaterandom access preambles. Then, the terminal selects a subframecorresponding to a PRACH configuration index. The terminal transmits theselected random access preamble in the selected subframe.

The base station receiving the random access preamble transmits a randomaccess response (PAR) to the terminal in operation S120. The randomaccess response is detected in two steps. First, the terminal detects aPDCCH masked with random access (RA)-RNTI. The terminal receives arandom access response in a Medium Access Control (MAC) Protocol DataUnit (PDU) on a PDSCH indicated by the detected PDCCH.

FIG. 3 is a view of a random access response.

The random access response may include TAC, UL grant, and temporaryC-RNTI.

The TAC is information indicating a time alignment value transmittedfrom a base station to a terminal in order to maintain UL timealignment. The terminal updates the UL transmission timing by using thetime alignment value. Once updating the time alignment, the terminalstarts or restarts a Time Alignment Timer.

The UL grant includes UL resource allocation and a transmit powercommand (TPC), which are used for the transmission of a schedulingmessage that will be described later. The TPC is used for determiningtransmit power for a scheduled PUSCH.

Referring to FIG. 2 again, the terminal transmits a message, which isscheduled according to the UL grant in the random access response, tothe base station in operation S130.

Hereinafter, a random access preamble may be referred to as a messageM1, a random access response may be referred to as a message M2, and ascheduled message may be referred to as a message M3.

From now on, referring to paragraph 5 of 3GPP TS 36.213 V8.7.0(2009-05), UL transmit power in 3GPP LTE will be described.

A transmit power PPUSCH(i) for PUSCH transmission in a subframe i isdefined as follows.P _(PUSCH)(i)=min{P _(CMAX),10 log₁₀(M _(PUSCH)(i))+P _(O) _(_)_(PUSCH)(j)+α(j)PL+Δ _(TF)(i)+f(i)}  [Equation 1]

where P_(CMAX) is configured terminal transmit power and M_(PUSCH)(i) isa bandwidth of PUSCH resource allocation of an RB unit. P_(O) _(_)_(PUSCH)(j) is a parameter consisting of the sum of a cell specificfactor given in an upper layer P_(O) _(_) _(NOMINAL) _(_) _(PUSCH)(j)and a terminal specific factor P_(O) _(_) _(UE) _(_) _(PUSCH)(j) whenj=0 and 1. α(j) is a parameter given in an upper layer. PL is path lossestimation calculated by a terminal. Δ_(TF)(i) is a terminal specificparameter. f(i) is a terminal specific value obtained from TPC. min{A,B}is a function for outputting a smaller value of A and B.

A transmit power P_(PUCCH)(i) for PUCCH transmission in a subframe i isdefined as follows.P _(PUCCH)(i)=min{P _(CMAX) ,P _(O) _(_) _(PUCCH) +PL+h(n _(CQI) ,n_(HARQ))+Δ_(F) _(_) _(PUCCH)(F)+g(i)}  [Equation 2]

where P_(CMAX) and PL are the same as those in Equation 1. P_(O) _(_)_(PUCCH)(j) is a parameter consisting of the sum of a cell specificfactor given in an upper layer P_(O) _(_) _(NOMINAL) _(_) _(PUCCH)(j)and a terminal specific factor P_(O) _(_) _(UE) _(_) _(PUCCH)(j).h(n_(CQI), n_(HARQ)) is a value dependent on a PUCCH format. Δ_(F) _(_)_(PUCCH)(F) is a parameter given by an upper layer. g(i) is a terminalspecific value obtained from TPC.

A transmit power P_(SRS)(i) for SRS transmission in a subframe i isdefined as follows.P _(SRS)(i)=min{P _(CMAX) ,P _(SRS) _(_) _(OFFSET)+10 log₁₀(M _(SRS))+P_(O) _(_) _(PUSCH)(j)±α(j)PL+f(i)}  [Equation 3]

where P_(CMAX), P_(O) _(_) _(PUSCH)(j), α(j), PL and f(i) are the sameas those in Equation 1. P_(SRS) _(_) _(OFFSET) represents a terminalspecific parameter given in an upper layer, and M_(SRS) represents abandwidth for SRS transmission.

Hereinafter, a multiple carrier system will be described.

A 3GPP LTE system supports the case that a DL bandwidth and a ULbandwidth are configured differently, but this requires one componentcarrier (CC). The 3GPP LTE system supports up to 20 MHz, and supportsonly one CC to each of UL and DL when a UL bandwidth and a DL bandwidthare different.

Spectrum aggregation (or, referred to as bandwidth aggregation andcarrier aggregation) supports a plurality of CCs. For example, if fiveCCs are allocated as granularity of a carrier unit having a 20 MHzbandwidth, the 3GPP LTE system may support the maximum bandwidth of 100Mhz.

One DL CC or a pair of a UL CC and a DL CC may correspond to one cell.Accordingly, a terminal communicating with a base station through aplurality of DL CCs may receive service from a plurality of servingcells.

FIG. 4 illustrates an example of a multiple carrier.

There are three DL CCs and three UL CCs, but their numbers are notlimited thereto. In each DL CC, a PDCCH and a PDSCH are separatelytransmitted, and in each UL CC, a PUCCH and a PUSCH are separatelytransmitted. Since three pairs of DL CCs-UL CCs are defined, a terminalmay receive service from three serving cells.

A terminal may monitor a PDCCH in a plurality of DL CCs, andsimultaneously may receive a DL transmission block through a pluralityof DL CCs. A terminal may transmit a plurality of UL transmission blockssimultaneously through a plurality of UL CCs.

It is assumed that a pair of DL CC #1 and UL CC #1 becomes a firstserving cell, a pair of DL CC #2 and UL CC #2 becomes a second cell, anda DL CC #3 becomes a third serving cell. Each serving cell may beidentified through a Cell index (CI). The CI may be unique in a cell orUE-specific. Here, the example that CI=0, 1, 2 are assigned to the firstto third serving cells is shown in FIG. 4.

The serving cell may be divided into a primary cell (PCell) and asecondary cell (SCell). The primary cell operates in a primaryfrequency, and is a cell designated as a primary cell when a terminalperforms an initial connection establishing process or starts aconnection re-establishing process, or performs a hand-over process. Theprimary cell is also called a reference cell. The secondary cell mayoperate in a secondary frequency, may be configured after RRC connectionis established, and may be used for providing an additional radioresource. At least one primary cell is always configured, and asecondary cell may be added/edited/released by an upper layer signaling(for example, an RRC message).

The CI of a primary cell may be fixed. For example, the lowest CI may bedesignated as the CI of a primary cell. Hereinafter, the CI of a primarycell is 0 and the CI of a secondary cell is sequentially allocated from1.

A terminal may monitor a PDCCH through a plurality of serving cells.However, even when there are N number of serving cells, a base stationmay be configured to monitor a PDCCH for the M (M<N) number of servingcells. Additionally, a base station may be configured to first monitor aPDCCH for the L (L<M<N) number of serving cells.

Even if a terminal supports a plurality of serving cells in an existing3GPP LTE, one Timing Alignment (TA) value may be commonly applied to aplurality of serving cells. However, a plurality of serving cells aregreatly far from a frequency domain, so that their propagationcharacteristics may vary. For example, in order to expand coverage orremove coverage hole, a Remote Radio Header (RRH) and devices may existin an area of a base station.

FIG. 5 illustrates a UL propagation difference between a plurality ofcells.

A terminal receives service through a primary cell and a secondary cell.The primary cell provides service by a base station and the secondarycell provides service by an RRH connected to a base station. Thepropagation delay characteristics of the primary cell and the secondarycells may vary due to the reasons such as the distance between a basestation and an RRH and a processing time of an RRH.

In this case, when the same TA value is applied to the primary cell andthe secondary cell, it may have a significant impact on the alignment ofa UL signal.

FIG. 6 illustrates an example of when a TA between a plurality of cellsis changed.

An actual TA of a primary cell is ‘TA 1’ and an actual TA of a secondarycell is ‘TA 2’. Accordingly, it is necessary that a separate TA shouldbe applied to each serving cell.

In order to apply a separate TA, a TA group is defined. The TA groupincludes one or more cells to which the same TA is applied. TA isapplied by each TA group, and a time alignment timer operates by each TAgroup.

Hereinafter, in consideration of two serving cells (i.e. a first servingcell and a second serving cell), a first serving cell belongs to a firstTA group and a second serving cell belongs to a second TA group. Thenumbers of serving cells and TA groups are for exemplary purposes only.The first serving cell may be a primary or secondary cell, and thesecond serving cell may be a primary or secondary cell.

A TA group may include at least one serving cell. A base station maynotify Information on a configuration of a TA group to a terminal.

Even if a terminal supports a plurality of serving cells in an existing3GPP LTE/LTE-A system, a single power amplifier may be used for ULtransmission. When each UL channel is transmitted in different servingcells, a radio frequency (RF) signal component between cells may not beeasily blocked. Especially, when ULs having a big transmit powerdifference are transmitted simultaneously from another cell, the aboveissue may become serious. Accordingly, simultaneous transmissions ofheterogeneous UL channels are difficult.

However, when it is assumed that TA groups are relatively apart greatlyon a frequency, a terminal may be implemented to use a separate poweramplifier in order for the UL transmission from each TA group.

Hereinafter, a method of transmitting a plurality of UL channels in aplurality of TA groups will be suggested.

Even when UL channels have different formats or the same format betweena plurality of TA groups, a UL channel such as a PUCCH having relativelylarge transmit power may be transmitted in the same UL subframe. Forexample, a terminal transmits a PRACH to a first serving cell andsimultaneously transmits a PUCCH/PUSCH/SRS to a second serving cell. Or,a terminal transmits an SRS to a first serving cell and simultaneouslytransmits a PUCCH/PUSCH to a second serving cell.

According to a current 3GPP LTE, a PRACH may not be transmitted in thesame subframe simultaneously together with a PUCCH/PUSCH/SRS. Accordingto the suggested present invention, if a plurality of TA groups areconfigured, a terminal may transmit a PUCCH/PUSCH/SRS to a serving cellbelonging to another TA group in the same subframe as the PRACH. Thatis, it is suggested that UL channels unavailable for simultaneoustransmission in the same TA group allows simultaneous transmission inanother TA group. A base station may notify whether simultaneoustransmission is allowed between a plurality of TA groups to a terminalthrough an RRC message.

FIG. 7 illustrates UL transmission according to an embodiment of thepresent invention. A PRACH (or a random access preamble) may betransmitted in one cell of each TA group. A first serving cell belongsto a first TA group and a second serving cell belongs to a second TAgroup.

When a PRACH is transmitted to the first serving cell, a UL channel,that is, at least one of a PUSCH, a PUCCH, and an SRS may be transmittedto the second serving cell. If a radio resource where a PRACH istransmitted and a radio resource where a UL channel is transmitted areoverlapped, total transmit power is required not to exceed theconfigured maximum transmit power in an overlapping portion. When aPRACH is transmitted to a first serving cell and a PUCCH is transmittedto a second serving cell, let's assume that one of OFDM symbols in whicha PRACH is transmitted and one of OFDM symbols in which a PUCCH istransmitted overlap. If the total transmit power of the PRACH and thePUCCH in the OFDM symbol does not exceed maximum transmit power, thePRACH and the PUCCH are transmitted in the overlapping OFDM symbol.

In other cells within a TA group that the first serving cell belongs, ULchannels may not be transmitted.

Within each TA group in one subframe, a PUCCH may be transmitted to onecell (or a primary cell of a specific TA group) in each TA group. Inother cells within a corresponding TA group, a PRACH/SRS/PUSCH may notbe transmitted, but in cells belonging to another TA group aRPRACH/SRS/PUSCH may be transmitted.

Within each TA group in one subframe an SRS and/or a PUSCH may not besimultaneously transmitted through the same OFDM symbol in differentcells of each TA group. In cells belonging to another TA group an SRSand/or a PUSCH may be transmitted on the same OFDM symbol.

Within each TA group in one subframe a PUCCH may not be simultaneouslytransmitted to different cells within each TA group but in cellsbelonging to another TA group a PUCCH may be simultaneously transmitted.Within each TA group in one subframe a PUCCH format may not besimultaneously transmitted to different cells in each TA group, but incells belonging to another TA group a PUCCH may be simultaneouslytransmitted. Within each TA group in one subframe different PUCCHformats may not be simultaneously transmitted to different cells in eachTA group, but in cells belonging to another TA group different PUCCHformats may be simultaneously transmitted.

A base station may notify a terminal, through RRC signaling, aboutwhether a specific UL channel between the above-described TA groups or aUL physical channel format group is simultaneously transmitted.

A UL channel carrying uplink control information (UCI) such as CSI andACK/NACK for each TA group may be transmitted to only a cell belongingto a corresponding TA group.

FIG. 8 illustrates UL transmission according to an embodiment of thepresent invention.

A first serving cell belongs to a first TA group and a second servingcell belongs to a second TA group. An issue is raised when a radioresource used for the transmission of an SRS in the first serving celland a radio resource used for the transmission of the UL channel of thesecond serving cell (i.e. at least one of a PUSCH, a PUCCH, and a PRACH)overlap partially or entirely. An SRS may include a periodic SRS and anaperiodic SRS.

For example, the transmission of an SRS is triggered in the last OFDMsymbol in a subframe n of the first serving cell and a PUCCH istransmitted in a subframe m+1 of the second serving cell, due todifferent TAs, the last OFDM symbol of the subframe n and the first OFDMsymbol of the subframe m+1 may overlap partially or entirely.

According to an embodiment, if there is the overlapped portion, SRStransmission may be dropped. If an OFDM used for SRS transmission and anOFDM used for UL channel transmission overlap partially, SRStransmission is abandoned.

According to another embodiment, if there is the overlapped portion andthe total transmit power of an SRS and a UL channel exceeds theconfigured maximum transmit power, SRS transmission may be dropped. Ifthe total transmit power of an SRS and a UL channel does not exceed theconfigured maximum transmit power, an SRS and a UL channel may betransmitted.

According to further another embodiment, if there is the overlappedportion and the total transmit power of an SRS and a UL channel exceedsthe configured maximum transmit power, SRS transmission may not bedropped but SRS transmit power may be reduced in order to allow thetotal transmit power not to exceed the maximum transmit power.

Since an aperiodic SRS dynamically scheduled by a base station is forthe base station to obtain a UL channel state at a specific point, itmay be more important than another UL channel. Accordingly, when anaperiodic SRS is triggered, it needs to be treated differently from aperiodic SRS.

According to an embodiment, if there is the overlapped portion, anaperiodic SRS is transmitted and the transmission of another UL channelin the overlapped portion may be dropped. Additionally, the transmissionitself of a UL channel may be abandoned. The UL channel may include aPUCCH carrying CSI.

According to another embodiment, if there is the overlapped portion, anaperiodic SRS is transmitted and the transmit power of another ULchannel in the overlapped portion is lowered not to exceed the maximumtransmit power. Or, transmit power may be identically lowered all overOFDM symbols where a UL channel is transmitted. The UL channel mayinclude a PUCCH carrying CSI.

FIG. 9 illustrates UL transmission according to another embodiment ofthe present invention.

If a TA difference between two TA groups is greater than an SRS transmitinterval, an SRS may not overlap a UL channel transmitted in anothercell.

Although SRS transmission is triggered on the last OFDM symbol of asubframe n in a first serving cell and a PUCCH is transmitted in asubframe m of a second serving cell, if an OFDM symbol for an SRS and anOFDM symbol for a PUCCH do not overlap, an SRS may be transmitted

FIG. 10, including view (a) and view (b). illustrates PUSCH and SRStransmission according to a typical technique.

When a terminal transmits an SRS on the last OFDM symbol of onesubframe, a PUSCH is not transmitted on the last OFDM symbol. This is toreduce the complexity of terminal UL transmission and changes inamplitude according to UL transmission.

In FIG. 10(a), a PUSCH is transmitted over all OFDM symbols in asubframe in which an SRS is not transmitted. In FIG. 10(a), when an SRSis transmitted on the last OFDM symbol, it is transmitted over all OFDMsymbols except for the last OFDM symbol.

However, when a terminal transmits a UL signal through cells belongingto different TA groups, this operation may cause problems.

FIG. 11 illustrates PUSCH and SRS transmission when a plurality of TAgroups are configured.

When a terminal transmits at least one of PUSCH/PUCCH/PRACH in asubframe n+1 of a first serving cell and transmits an SRS on the lastOFDM symbol in a subframe n of a second serving cell, let's assume thatthere is an overlapped portion.

When total transmit power exceeds the maximum transmit power in theoverlapped portion, SRS transmission may be abandoned. As a result,since a terminal does not transmit an SRS in a subframe n of a secondserving cell, as shown in FIG. 11, a PUSCH is transmitted over all OFDMsymbols.

A base station may not accurately determine transmission timing betweena first TA group that a first serving cell belongs and a second TA groupthat a second serving cell belongs. Additionally, the base station maynot determine whether the total transmit power of a terminal exceeds themaximum transmit power. Accordingly, the base station may not accuratelydetermine whether there is an overlapped portion and SRS transmission isdropped. Accordingly, when whether a symbol of a PUSCH is transmitted ona corresponding OFDM symbol is determined according to whether aterminal actually transmits an SRS, a base station may have a difficultyin receiving the PUSCH.

Additionally, even if there is an overlapped portion between differentTA groups, when it is allowed that a UL signal different from an SRS istransmitted simultaneously, the same difficulty may occur if totaltransmit power exceeds the maximum transmit power and SRS transmissionis abandoned.

FIG. 12 illustrates UL transmission according to another embodiment ofthe present invention.

Regardless of whether a terminal actually transmits an SRS in a subframeconfigured to transmit an SRS, it is suggested that a PUSCH is nottransmitted in an SRS symbol.

Or, with respect to all SRS subframes configured to transmit an SRS byeach cell or each TA group, a PUSCH may not be transmitted on acorresponding SRS symbol regardless of whether a terminal transmits anSRS.

Regardless of whether there is the overlapped portion, a PUSCH may notbe transmitted in a corresponding SRS symbol.

In order to transmit a PUSCH except for an SRS symbol, a code sequenceto be transmitted in a PUSCH may be excluded from a generationoperation, or after a code sequence is generated under the assumptionthat a PUSCH is transmitted to a corresponding SRS symbol, the codesequence may not be mapped into a corresponding symbol.

Hereinafter, the transmission of a channel (for example,PUCCH/PUSCH/SRS) different from a PRACH will be described.

When a terminal configured with a first TA group and a second TA grouptransmits a PRACH to a first serving cell (for example, a secondarycell) belonging to the first TA group and a UL channel to a secondserving cell belonging to the second TA group, if the total transmitpower of a PRACH and a UL channel exceeds the maximum transmit power, itis necessary to adjust transmit power or abandon transmission.

In a first embodiment, a priority may be put on power allocation in theorder of a PUCCH of a primary cell, a PUSCH having UCI, a PRACH of asecondary cell, and another channel, From a channel having a lowpriority, transmit power is reduced or transmission is abandoned,thereby adjusting total transmit power not to exceed the maximumtransmit power.

In a second embodiment, a high priority may be put on a UL channeltransmitted through a TA group that a primary cell belongs. Let's assumethat a first serving cell belonging to a first TA group is a secondarycell and a second serving cell belonging to a second TA group is aprimary cell. When UL channels are simultaneously transmitted to thefirst and second serving cells, the transmit power of a UL channeltransmitted to the first serving cell may be reduced first or itstransmission may be abandoned.

In a third embodiment, a higher priority may be put on another ULchannel than a PRACH transmitted to the secondary cell. When thetransmission of a PRACH to the secondary cell and the transmission of aUL channel to a cell of another TA group overlap, the transmit power ofthe PRACH may be reduced first or its transmission may be abandoned.

In a fourth embodiment, a higher priority may be put on a PRACH. Thereason is that when the transmission of the PRACH is failed, the ULalignment of a corresponding TA group may be delayed. When thetransmission interval of a UL channel and the transmission interval of aPRACH overlap, transmit power may be reduced only in the overlappedportion.

In a fifth embodiment, a lower priority may be put on a PRACH. Like aPRACH transmitted through UpPTS in a 3GPP LTE TDD system, there is aPRACH having a short transmission short (this is called ashortened-PRACH (sPRACH). At this point, an entire transmission intervalof a PRACH may overlap an entire or part of the transmission interval ofa UL channel. When total transmit power exceeds the maximum transmitpower, it is inefficient to abandon UL channel transmission or reducethe transmit power of a UL channel.

Transmission may be abandoned or transmit power may be reduced only in atransmission interval overlapping a sPRACH in a corresponding ULchannel. The UL channel may be a PUCCH or a PUSCH having CSI.

Or, sPRACH transmission may be abandoned or its transmit power may bereduced. A UL channel overlapping a sPRACH may be a PUCCH havingACK/NACK.

FIG. 13 is a block diagram of a wireless communication system accordingto an embodiment of the present invention.

A base station 50 includes a processor 51, a memory 52, and a radiofrequency (RF) unit 53. The memory 52 is connected to the processor 51and stores a variety of information for operating the processor 51. TheRF unit 53 is connected to the processor 51 to transmit and/or receive aradio signal. The processor 51 implements suggested functions,processes, and/or methods. In the above-described embodiments, theserving cell and/or the TA group may be controlled/managed by a basestation, and also, operations of one or more cells may be implemented bythe processor 51.

The wireless device 60 includes a processor 61, a memory 62, and an RFunit 63. The memory 62 is connected to the processor 61 and stores avariety of information for operating the processor 61. The RF unit 63 isconnected to the processor 61 to transmit and/or receive a radio signal.The processor 61 implements suggested functions, processes, and/ormethods. In the above-described embodiments, operations of a terminalmay be implemented by the processor 61.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method for uplink transmission in a wirelesscommunication system, the method performed by a user equipment (UE) andcomprising: determining whether to drop a sounding reference signal(SRS) on a last symbol in a i^(th) subframe, wherein the SRS is droppedif multiple timing advance groups (TAGs) are configured, if a portion ofthe last symbol of the i^(th) subframe for transmitting the SRS toward afirst serving cell in a first TAG is overlapped with an (i+1)^(th)subframe for transmitting an uplink channel toward a second serving cellin a second TAG and if a total power of the SRS and the unlink channelexceeds a maximum value on the overlapped portion of the last symbol. 2.The method of claim 1, further comprising: determining, by the UE, apower for transmitting the SRS toward the first serving cell in thefirst TAG; and determining, by the UE, a power for transmitting theuplink channel toward the second serving cell in the second TAG.
 3. Themethod of claim 1, further comprising: starting a first time alignmenttimer for the TAG; and starting a second time alignment timer for thesecond TAG.
 4. The method of claim wherein the uplink channel includesat least one of a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a random access channel.
 5. The methodof claim 1, further comprising: receiving a periodic configurationindicating a SRS periodicity and a SRS subframe offset, wherein thei^(th) subframe is determined bused on the periodic configuration. 6.The method of claim 1, further comprising: receiving a request for theSRS transmission.
 7. A user equipment (UE) for uplink transmission in awireless communication system, the UE comprising: a transceiverconfigured to transmit and receive radio signals; and a processoroperatively coupled with the transceiver and configured to: determinewhether to drop a sounding reference signal (SRS) on a last symbol in ai^(th) subframe, wherein the SRS is dropped if multiple timing advancegroups (TAGs) are configured, if a portion of the last symbol of thei^(th) subframe for transmitting the SRS toward a first serving cell ina first TAG is overlapped with an (i+1)^(th) subframe for transmittingan uplink channel toward a second serving cell in a second TAG and if atotal power of the SRS and the uplink channel exceeds a maximum value onthe overlapped portion of the last symbol.
 8. The UE of claim 7, whereinthe processor is further configured to: determine a power fortransmitting the SRS toward the first serving cell in the first TAG; anddetermine a power for transmitting the uplink channel toward the secondserving cell in the second TAG.
 9. The UE of claim 7, wherein theprocessor is father configured to: start a first time alignment timerfor the first TAG; and start a second time, alignment timer for thesecond TAG.
 10. The UE of claim 7, wherein the uplink channel includesat least one of a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a random access channel.
 11. The UE ofclaim 7, wherein the processor is further configured to: receive aperiodic configuration indicating a SRS periodicity and a SRS sub frameoffset, wherein the subframe i^(th) is determined based on the periodicconfiguration.
 12. The UE of claim 7, wherein the processor is furtherconfigured to receive a request for the SRS transmission.